Messages in this thread Patch in this message | | | Date | Thu, 22 Apr 2010 19:51:53 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH 04/14] mm,migration: Allow the migration of PageSwapCache pages |
| |
On Thu, 22 Apr 2010 19:31:06 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Thu, 22 Apr 2010 19:13:12 +0900 > Minchan Kim <minchan.kim@gmail.com> wrote: > > > On Thu, Apr 22, 2010 at 6:46 PM, KAMEZAWA Hiroyuki > > <kamezawa.hiroyu@jp.fujitsu.com> wrote: > > > > Hmm..in my test, the case was. > > > > > > Before try_to_unmap: > > > mapcount=1, SwapCache, remap_swapcache=1 > > > After remap > > > mapcount=0, SwapCache, rc=0. > > > > > > So, I think there may be some race in rmap_walk() and vma handling or > > > anon_vma handling. migration_entry isn't found by rmap_walk. > > > > > > Hmm..it seems this kind patch will be required for debug. > >
Ok, here is my patch for _fix_. But still testing... Running well at least for 30 minutes, where I can see bug in 10minutes. But this patch is too naive. please think about something better fix.
== From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
At adjust_vma(), vma's start address and pgoff is updated under write lock of mmap_sem. This means the vma's rmap information update is atoimic only under read lock of mmap_sem.
Even if it's not atomic, in usual case, try_to_ummap() etc... just fails to decrease mapcount to be 0. no problem.
But at page migration's rmap_walk(), it requires to know all migration_entry in page tables and recover mapcount.
So, this race in vma's address is critical. When rmap_walk meet the race, rmap_walk will mistakenly get -EFAULT and don't call rmap_one(). This patch adds a lock for vma's rmap information. But, this is _very slow_. We need something sophisitcated, light-weight update for this..
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> --- include/linux/mm_types.h | 1 + kernel/fork.c | 1 + mm/mmap.c | 11 ++++++++++- mm/rmap.c | 3 +++ 4 files changed, 15 insertions(+), 1 deletion(-)
Index: linux-2.6.34-rc4-mm1/include/linux/mm_types.h =================================================================== --- linux-2.6.34-rc4-mm1.orig/include/linux/mm_types.h +++ linux-2.6.34-rc4-mm1/include/linux/mm_types.h @@ -183,6 +183,7 @@ struct vm_area_struct { #ifdef CONFIG_NUMA struct mempolicy *vm_policy; /* NUMA policy for the VMA */ #endif + spinlock_t adjust_lock; }; struct core_thread { Index: linux-2.6.34-rc4-mm1/mm/mmap.c =================================================================== --- linux-2.6.34-rc4-mm1.orig/mm/mmap.c +++ linux-2.6.34-rc4-mm1/mm/mmap.c @@ -584,13 +584,20 @@ again: remove_next = 1 + (end > next-> if (adjust_next) vma_prio_tree_remove(next, root); } - + /* + * changing all params in atomic. If not, vma_address in rmap.c + * can see wrong result. + */ + spin_lock(&vma->adjust_lock); vma->vm_start = start; vma->vm_end = end; vma->vm_pgoff = pgoff; + spin_unlock(&vma->adjust_lock); if (adjust_next) { + spin_lock(&next->adjust_lock); next->vm_start += adjust_next << PAGE_SHIFT; next->vm_pgoff += adjust_next; + spin_unlock(&next->adjust_lock); } if (root) { @@ -1939,6 +1946,7 @@ static int __split_vma(struct mm_struct *new = *vma; INIT_LIST_HEAD(&new->anon_vma_chain); + spin_lock_init(&new->adjust_lock); if (new_below) new->vm_end = addr; @@ -2338,6 +2346,7 @@ struct vm_area_struct *copy_vma(struct v if (IS_ERR(pol)) goto out_free_vma; INIT_LIST_HEAD(&new_vma->anon_vma_chain); + spin_lock_init(&new_vma->adjust_lock); if (anon_vma_clone(new_vma, vma)) goto out_free_mempol; vma_set_policy(new_vma, pol); Index: linux-2.6.34-rc4-mm1/kernel/fork.c =================================================================== --- linux-2.6.34-rc4-mm1.orig/kernel/fork.c +++ linux-2.6.34-rc4-mm1/kernel/fork.c @@ -350,6 +350,7 @@ static int dup_mmap(struct mm_struct *mm goto fail_nomem; *tmp = *mpnt; INIT_LIST_HEAD(&tmp->anon_vma_chain); + spin_lock_init(&tmp->adjust_lock); pol = mpol_dup(vma_policy(mpnt)); retval = PTR_ERR(pol); if (IS_ERR(pol)) Index: linux-2.6.34-rc4-mm1/mm/rmap.c =================================================================== --- linux-2.6.34-rc4-mm1.orig/mm/rmap.c +++ linux-2.6.34-rc4-mm1/mm/rmap.c @@ -332,11 +332,14 @@ vma_address(struct page *page, struct vm pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); unsigned long address; + spin_lock(&vma->adjust_lock); address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT); if (unlikely(address < vma->vm_start || address >= vma->vm_end)) { + spin_unlock(&vma->adjust_lock); /* page should be within @vma mapping range */ return -EFAULT; } + spin_unlock(&vma->adjust_lock); return address; }
-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |